DC-to-DC converters typically are designed as switching regulated power supplies, also known as switch-mode power supplies. Some DC-to-DC converters raise voltage from a lower input voltage (step-up converters), and others lower voltage from a higher input voltage (step-down converters). One type of step-down switch mode power supply is known as a Buck converter. These devices resemble linear power supplies in some respects, but in other ways are much different. A switching power supply typically includes an energy-storage inductor, and sometimes a non-linear regulator network. This type of power supply may incorporate a regulation system in which a control element, for example, a power MOSFET switch, is switched on and off rapidly. Controlling on/off pulses may be produced by an oscillator/error amplifier/pulse-width modulator network as a controller. Thus, in a more common variety of switching regulator, the transistor switch, for example, the MOSFET, is a control element.
During an ON cycle, energy may be pumped into an inductor and stored in a magnetic field. When the control element is turned OFF, the energy stored in the inductor is directed into a filter and load. Various sampling circuits may sample the output voltage and feed a sample to an input of an error amplifier as part of a controller. The sample voltage may be compared with a reference voltage and an error amplifier may increase its output control voltage, which may be sent to a pulse-width modulator. The pulse-width modulator may produce a modified ON/OFF signal, for example, a square wave whose ON and OFF times are determined by the input error voltage.
More specific examples of DC-to-DC converters as switch mode power supplies are disclosed in commonly assigned, published U.S. patent application nos. 2003/0038614 and 2004/0070382, which are incorporated by reference herein. As noted before, a Buck converter is a specific type of step-down, DC-to-DC converter.
To power various microprocessors, and more particularly the next generation microprocessors, which may require a voltage of about one volt at up to 1,000 amps, the number of phases in a multiphase Buck converter has been increasing, sometimes requiring as many as eight phases. The optimum number of phases may be determined by the output current, system efficiency, transient requirements, thermal management, cost of capacitors, MOSFET performance, size restrictions, and overall system costs. A controller for Buck converters may be complicated and typically is designed as a multiphase pulse-width modulation (PWM) control integrated circuit with companion gate drivers, e.g., the HIP6301, HIP6601B, HIP6602B, HIP6603B, or HIP6604B with external MOSFETs, for example, as manufactured by the assignee of the present invention, Intersil Americas Inc.
Multiphase power conversion is an improvement over earlier single phase converter configurations and is used to satisfy the increasing current demands of modern microprocessors. Multiphase converters distribute the power and load current, which results in smaller and lower cost transistors with fewer input and output capacitors. This occurs because of higher effective conversion frequency with higher frequency ripple current and phase interleaving. Each phase circuit typically includes a lower MOSFET and an upper MOSFET as power switches. The requirement for decreasing the size of the converter along with the requirement for higher power densities requires an increase in the switching frequency used in the power converter. The use of a high switching frequency in these multiphase DC-to-DC converters, and especially Buck converters, however, may lead to switching losses, stresses on the power component, and EMI generation.